test: bump up test timeout to 20m
test: bump up test timeout to 20m

Recently, we've added bunch of tests...

Signed-off-by: Gyuho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

vimalk78/etcd,joshix/etcd,rnaveiras/etcd,rnaveiras/etcd,mqliang/etcd,li-ang/etcd,sebrandon1/etcd,lorneli/etcd,sebrandon1/etcd,dannysauer/etcd,etcd-io/etcd,ajityagaty/etcd,glevand/coreos--etcd,sinsharat/etcd,etcd-io/etcd,ajityagaty/etcd,mkumatag/etcd,mqliang/etcd,li-ang/etcd,gyuho/etcd,sinsharat/etcd,lorneli/etcd,coreos/etcd,xiang90/etcd,bdarnell/etcd,etcd-io/etcd,mkumatag/etcd,coreos/etcd,fanminshi/etcd,cockroachdb/etcd,glevand/coreos--etcd,cockroachdb/etcd,fanminshi/etcd,xiang90/etcd,bdarnell/etcd,vimalk78/etcd,mqliang/etcd,ajityagaty/etcd,joshix/etcd,gyuho/etcd,dannysauer/etcd,mkumatag/etcd,rnaveiras/etcd